For implantation of prosthetic stems, such as hip stems, accurate preparation of the bone or intramedullary canal is extremely important in order to guarantee good contact between the prosthesis stem and the bone. Preparation of the bone canal for implantation of a prosthetic stem is presently prepared by drilling a resected end of a bone, such as a femur, and then preparing an area adjacent the drilled hole to provide a seat for the prosthetic stem.
Preparation of the area adjacent the drilled hole may be accomplished by broaching or by milling. Currently, however, milling has been identified as an extremely precise method of bone preparation in many orthopaedic applications as compared to broaching. Bone milling is currently thus the preferred method of bone preparation. The concept is that a precise bone envelope reduces the gaps between the implant (i.e. prosthesis or prosthetic component) and the bone, thereby improving the initial and long-term bone ingrowth/fixation.
A critical limitation of milling systems today is that they use straight reamers to remove bone. Straight reamers limit the geometry that can be created in the bone and thus the external geometry of the corresponding implant. A typical milling frame can be seen in U.S. Pat. No. 5,540,694 issued to DeCarlo, J. et al. on Jul. 30, 1996. This milling frame uses a straight reamer that is useable for various geometries. For example, the anatomy of the medial endosteum of the femur can be described as a curve. Many implant designs thus employ a medial curve to load this region. It is therefore desirable to have a device that can precisely mill the bone to allow for the medial curve as such would improve the accuracy of the bone preparation and thus the bone fixation. One way of preparing the bone along a curved path is to use a series of broaches.
Broaches, however, have serious limitations. One such limitation is the risk of fracture during broaching. Since broaching is done by pounding the broach into the bone, the bone tends to fracture.
In consideration of the above, there have been attempts to provide flexible medullary canal reamers. Such medullary canal reamers are used to enlarge the medullary canal of bones in preparation for the insertion of a prosthetic component, such as a total hip prosthesis. One such device is provided in U.S. Pat. No. 6,053,922 issued to Krause et al. on Apr. 25, 2000. Krause describes a flexible shaft for a reamer. The Krause shaft comprises a solid element with a longitudinal bore the entire length thereof, and a slot formed thereon that extends spirally around the shaft either continuously or segmentally. A problem, however, with the Krause flexible shaft is that Krause is only concerned with the shaft portion and not the cutting portion of the reamer. As such, the cutting geometry associated with the reamer and the Krause flexible shaft is no different than other embodiment of reamers. As well, other flexible shafts fall short for the same reasons.
Additionally, prior reamers have fixed input shafts for connecting to and/or receiving motive (i.e. rotary) power. As such, the prior reamers are able to accept rotary input power with respect to only one direction. Typically, this direction is at 0° (i.e. “straight on”). Therefore, not only is the input power direction restricted, but this, in turn, restricts the angle at which the reamer may be used on a patient.
In view of the above, it would be desirable to have a bone miller or guided reamer for preparing non-axisymmetric bone.
It would be further desirable to have a bone cutter that can mill complex bone geometries.
It would be still further desirable to have a bone cutting device that can mill bone along a curve, especially a curve of any radius of curvature.
It would be yet further desirable to have a bone cutter that can provide precise milling along any defined curve.
It would be even farther desirable to have a bone milling device as desired above that also is able to accept input rotary power from various angular orientations and/or allows bone milling device to be positioned at various angular orientations relative to the input rotary power.